This invention relates to microfilm readers and more particularly, microfilm readers having image rotation capability.
Microfilm has become a common media for storage and distribution of large amounts of information. Microfilm can reduce the storage area of paper documents by a hundred fold enabling large quantities of documents or graphical forms of information to be stored in a small space. The microfilm can take various storage configurations. One form is commonly referred to as microfilm jackets in which individual strips of film are placed between two transparent sheets having channels to accept and retain the film. A second form similar to microfilm jacket is microfiche, in which a piece of photoplastic material approximately four inches by six inches has the information photographed thereon. Microfiche can also be made by a duplicating process from an original microfilm jacket. The size of the microfiche can vary, however, the concept encompasses placing multiple images on a single card or fiche. Information may also be retained on rolls of microfilm which are stored in cartridges or cassettes for later retrieval.
Microfilm readers can take any one of several configurations depending on whether they are used to view flat microfilm, such as jackets or fiche, or roll microfilm which is stored in cartridges or cassettes. However, they are all similar in that they have a light projection system which concentrates a beam of light through the film, which in turn projects the image from the film onto a viewing surface. The orientation of the projected image is dependent upon the orientation of the image on the film.
Original source documents are microfilmed using any one of several types of microfilm cameras. One such type is a planetary microfilm camera in which the document is merely laid on a photographing surface which has a stationary camera mounted above or below it. A picture of the document is taken and the process is repeated for each source document. The film is developed after the documents are photographed and can either be placed in micorfilm jackets or placed in cartridges or cassettes. In another type of microfilming system, an automatic feeder sequentially feeds documents to a microfilming area and a stationary camera photographs each document. The feeder then moves the documents out of the photographing area and a new document is fed into the photographing area to be filmed. An example of such an automatic microfilm camera is illustrated in U.S. Pat. No. 4,148,579. In a last type of microfilming, a rotary microfilm recorder is used. In this type of filming apparatus, the documents are fed through a photographing area and the film is moved at the same time. Thus, while both the documents and film are actually moving, they are stationary with respect to each other. This type of microfilming is for high volume microfilming operations where a large number of documents must be microfilmed successively. An example of where such a recorder would be used is in the microfilming of checks at financial institutions.
A problem which has been encountered with planetary cameras or rotary microfilming systems is that the document is sometimes skewed when it is photographed. Thus, the image which results on the film is also at an angle with respect to the edge of the film. When the film is positioned for viewing, the images are projected at a skewed angle with respect to the horizontal. Likewise, the documents are sometimes inadvertently microflimed upside down with respect to adjacent documents giving rise to an image being projected upside down. This is an obvious nuisance to the operator who must remove, rotate and reinsert the microfilm upside down in order to view the projected image in its proper orientation. If the document is merely skewed, the operator can usually still read it although it might be awkward. In order to compensate for the various orientations of the original documents when they are photographed, it is desirable to rotate the image to orient it properly for the user when the images are projected. Generally, such image rotation is achieved by the use of a dove prism. One such example is illustrated in U.S. Pat. No. 3,649,119.
Some microfilm readers are equipped with two projection lenses which enables the projection of images in either of two magnifications, generally a low magnification and a high magnification. One example of where such a dual magnification microfilm reader is convenient is when the source document has a great deal of printed information photographed at a high magnification resulting in the printed images being relatively small when projected. The general subject matter can conveniently be found using the low magnification and when the particular information sought is to be read, the user can switch to the high magnification lens.
In prior art devices which utilize two projection lenses, image rotation devices such as the use of a dove prism, have not generally been made available. The reason is that a dove prism could only be mounted above one of the projection lenses and rotated while the other projection lens was not capable of image rotation. Thus, while one of the lenses could be rotated to present the image in its right-side-up, proper reading position, switching to the other projection lens would result in the same image now presented for viewing in its skewed or upside down position for reading. An additional problem is encountered by the use of only one prism above one lens. A prism inverts an image in a light path as a mirror does. If a prism is used only above one lens, but not both, one of the two lenses will project an inverted or "wrong reading" image when switching between the two lenses. These problems presented serious drawbacks relating to the use of image rotation devices on dual lens microfilm readers.
Applicant has attempted to solve these problems by providing a microfilm reader having dual projection lenses with prisms positioned above each of the lenses. Applicant's inventive device provides for rotating both prisms simultaneously, the same amount, which results in the amount of rotation of the projected image to be the same regardless of which projection lens is placed in the projection light path. The prism rotation is accomplished by mounting the prisms in cylindrical holders which are free to rotate above each of the projection lenses. The cylindrical holders are placed in a lens block assembly which can be moved to position either projection lens in the projection light path. A prism gear is formed around the outside diameter of the cylindrical prism holders and a drive mechanism is provided to rotate the prism holders. The drive mechanism causes the prism gears to rotate the prism holders in unison. The drive mechanism in turn is controlled by the operator of the microfilm reader. Thus, the operator simultaneously rotates both of the prisms, in unison, a like amount. This results in the projected image being placed in the same orientation regardless of which projection lens is placed in the image projection path.